The California Environmental Authority (CARB) as well as United States federal authorities require an onboard diagnosis of the tank system in motor vehicles. Here, leaks of a specific size (for example, leaks greater than 1 mm in diameter) are to be detected.
U.S. Pat. No. 5,390,645 discloses an arrangement for checking the tightness of a motor vehicle tank system wherein the tightness check is performed with the aid of a pump volume flow divided into two paths. A first path is connected to the motor vehicle tank system; whereas, the second path is connected to the atmosphere via a reference leak in the form of a flow resistor of a specific size.
A flow sensor is installed in each of the paths and detects the flow along the corresponding path. A conclusion is drawn in an electronic circuit device as to the presence of a leak or the non-presence thereof based on a flow difference in the two paths.
Disadvantages are present with respect to this arrangement. On the one hand, two separate comparatively complex flow sensors are required in addition to the electronic circuit arrangement. Furthermore, the pump in this arrangement is only used for diagnostic purposes. However, a diagnosis is performed only rarely (approximately 1% of the entire driving operation). For this reason, the pump therefore has a disadvantageously low degree of use.